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Just a few in the US - and they were all different at that time. They were all intertwined with politics at their time. Quick google search though, not sure how good the sources are:
Railroad: https://digfir-published.macmillanusa.com/roark7e/roark7e_ch18_4.html
Steel, oil, and tobacco: https://19thcentury.us/19th-century-monopolies/
Or just recently: take a look at China. How Chinese Big Tech influence on society was crushed and control was taken back by the Communist Party in the past 5 years.